The present invention relates to a method of making a free-flowing agglomerated powder detergent containing high levels of nonionic surfactant.
Most granular detergents are produced by spray drying. This process involves mixing detergent components such as surfactants and builders with water to form a slurry which is then sprayed into a high temperature air stream to evaporate excess water and to form bead-type hollow particles. While spray drying the detergent slurry produces a hollow granular detergent having an excellent solubility, extremely large amounts of heat energy are needed to remove the large amounts of water present in the slurry. Another disadvantage of the spray drying process is that because large scale production equipment is required, a large initial investment is necessary. Further, because the granules obtained by spray drying have a low bulk density, the granule packaging volume is large which increases costs and paper waste. Also, the flowability and appearance of the granules obtained by spray drying is poor because of the presence of large irregularities on the surface of the granules.
In addition to these characteristic processing and product problems associated with the spray drying process, volatile materials, such as nonionic surfactants, are emitted into the air when processed by this method with the other detergent components. This volatilization problem, manifested by the discharge of dense "blue" smoke from the spray tower, is referred to as "plumbing." Air pollution standards limit the opacity of the plume. Consequently, it is necessary to limit the capacity of the spray tower or, in extreme instances, discontinue operation.
Other suggested methods call for post-dosing the product with nonionic surfactant after the spray drying operation. Unfortunately, post-dosing of the spray dried base with surfactant in amounts sufficient to provide satisfactory wash performance generally results in poor flowing, aesthetically displeasing products. Accordingly, the amount of surfactant that may be employed in the detergent formulation is severely limited. Because heavy-duty laundry detergents need large amounts of nonionic surfactant present, inorganic silicates have been added to these detergent formulations to absorb the nonionic liquids.
U.S. Pat. No. 3,769,222 to Yurko et al. discloses mixing liquid nonionic surfactants with sodium carbonate until partial solidification occurs followed by the addition of large amounts of silica (silicon dioxide) to produce a dry free-flowing detergent composition. A disadvantage to this technique, however, is that because the silica has no significant cleaning activity, its inclusion in a detergent formulation in large amounts merely serves to increase the cost of the product. Further, the use of silica in detergents adds to the total suspended solids (TSS) content of laundry waste water contrary to the dictates of many local and state water pollution standards. Therefore, there is an incentive to keep low the amount of silica added to the detergent composition.
U.S. Pat. No. 4,473,485 to Greene reports that a free-flowing granular detergent can be prepared by mixing a polycarboxylic structuring agent solution with a micronized sodium carbonate as a builder and a flow agent, followed by the addition to the mixture of a nonionic surfactant and water, followed by removal of the excess water. A disadvantage of this process, however, is that the removal of excess water from the detergent powder requires additional processing time and generally requires the consumption of heat energy. Another significant disadvantage of this process is that the micronized sodium carbonate used by Greene to enhance the flowability of the detergent product is quite expensive as compared to standard sodium carbonate. Without the use of the micronized sodium carbonate, Greene's product would not have such good flowability.
While various attempts have been made to produce granular detergent compositions by methods other than spray drying, these methods have not alleviated all of the problems completely. For example, some methods contemplate the addition of binders to agglomerate the powder particles. Typically, premixed ingredients are tumbled in a large drum while binder solution is sprayed onto the tumbling particles. These methods suffer from the problems of wide particle size distribution of the resulting particles and poor water solubility.
In both spray drying processes and agglomeration processes, ingredients must first be mixed and then treated in a separate operation to effect granulation, i.e., either a spray drying operation or an agglomerating operation. Therefore, there is a need to find a new method for producing a highly loaded nonionic detergent composition having enhanced flowability, product appearance, water solubility and water dispersibility while minimizing the attendant fire, air and water pollution hazards as well as the foregoing processing disadvantages.